During erythropoiesis, maturing erythroblasts form adhesive interactions with extracellular matrix components and with other bone marrow cells in their local microenvironment. It is known that clusters of erythroblasts rely on such interactions for optimal cell maturation, but the precie role of the erythropoietic microenvironment in supporting and modulating erythroid maturation is unclear. Integrins in the cell membrane are the key mediators of erythroblast cell-cell and cell-matrix interactions. In addition to promoting adhesion interactions, integrins mediate bidirectional signaling (outside-in and inside-out) between the extracellular and intracellular environments of the erythroblast. Integrins are also important mediators of cytoskeletal reorganization, a process that is central to the structural changes occurring in the terminal stages of erythroid maturation. Here, we propose to measure the membrane dynamics of the major erythroblast integrins, define the molecular regulation of integrin-mediated erythroblast adhesion interactions, and characterize the links between integrin dynamics and cytoskeletal reorganization. We will also investigate the relationship between integrin-driven signaling and erythropoietin-driven signaling, which could work together to optimize erythropoiesis under homeostatic and/or stress conditions. Our ultimate goal is to understand the impact of integrin-dependent functions on erythropoiesis. Our laboratory is ideally suited to undertake these endeavors, having at our disposal multiple advanced, quantitative single-molecule and single-cell imaging techniques as well as expertise in multicolor flow cytometry and mouse models. Based on our preliminary data, we hypothesize that erythroblast integrin dynamics and signaling both modulate and are governed by erythroid maturation and that integrin-mediated events interact with erythropoietin-directed signaling in this process. In Aim 1, we will characterize the membrane dynamics of integrins on the maturing erythroblast, define how such dynamics are controlled by ligand engagement and cytoskeletal reorganization, and elucidate the regulation of intracellular signaling pathways by these dynamics. In Aim 2, we will characterize mechanisms of potential interaction between erythropoietin-dependent pathways and integrin-dependent pathways that regulate terminal erythroid maturation. Successful completion of this project will provide new insights into the mechanisms underlying erythroid development and may aid in the identification of novel targets for therapeutic intervention in disorders of erythropoiesis. (End of Abstract)